Incorporation of Ground-Fault Protection Devices (GFPD) for traditional implementation of centralized inverter based photovoltaic (PV) solar energy systems have become mandatory after early incidences of fire which were later shown could be avoided have there been such protective devices installed. Ground Fault Circuit Interrupters (GFCI), Arc Fault Circuit Interrupters (AFCI), Leakage Current Detector Interrupters (LCDI), Equipment Ground Fault Protective Devices (EGFPD), Appliance Leakage Current Interrupters (ALCI) and Immersion Detection Circuit Interrupters (MCI) are used for such protection in a variety of systems. These devices typically sense or determine the leakage current and trigger a safe shut-off and de-energize the system.
Similar studies are being performed for detection and extinguishing of arcs in PV Systems. Arc Fault Circuit Interrupters monitor the current through various paths and voltages at various nodes in the systems, respectively. These signals are first passed through a signal conditioning chain and are digitized through an analog-to-digital converter (ADC). Next, these signals are processed by a digital signal processor (DSP) or custom hardware where it compares with various pre-determined criterion including pre-established signatures to detect an arcing event in the system. If an arcing event is detected systematic automatic triggering of the power switches is accomplished to first extinguish the arc, and then to de-energize the entire system or portions of it.
In traditional solar power plants, where each of the solar modules in a string are connected in series, mismatches among the solar modules lead to degraded performance of total energy harvest. In a typical environment it has been demonstrated that varying shadowing and mismatch related issues among the solar modules lead to up to 25% of lost energy.
Recently, various technologies have been developed to solve these problems. In particular, Microinverter and Power Optimizer technologies improve the system performance by embedding electronics close to each of the solar panels. In the case of microinverters, the energy harvested from the individual solar module is converted to AC, which is suitable for directly feeding into the power system grid. In case of the optimizer, each of the solar modules consists of a DC-DC converter. The outputs of the DC-DC converters are then connected in series to form a string of solar modules, which are then fed into a centralized inverter for converting to AC suitable for feeding into the grid.
In either case of the microinverters and power optimizers, the individual solar modules are decoupled from each other, and are operated at their maximum power point thus allowing maximum possible energy harvest. Each of the solar modules have their individual maximum power point due to their own individual operating conditions specific to the extent to which the solar module is soiled or shadowed.
The microinverter and power optimizer technologies provide further advantage by allowing module level diagnostics and monitoring. Each of the modules can have bi-directional communication capability using either power-line, wireless or traditional wire-line communication technologies. This allows diagnostics and monitoring of various parameters associated with each of the modules and the corresponding electronics. In some cases, the module integrated electronics may have one or many of the following features: communication, diagnostics, monitoring and safety. In such cases, the module electronics are not capable of performing power conditioning for decoupling the solar array string from the module, however, they can continue to perform key GFCI and AFCI Capabilities.
Irrespective of such distributed implementation of various electronic capabilities inside the solar module, GFCI and AFCI techniques have continued to rely on traditional techniques. In such techniques, a combination of DC or AC Disconnect and a Centralized Inverter Integrated or external GFCI device is used to comply with the regulatory code. Such techniques typically have limited resolution thus limit the safety trigger points only to higher values of critical signals. High resolution implementations are available, however, could be inordinately expensive and difficult to install.